If the error still occurs then the following MailEnable registry keys can be
altered:

MailEnable
has the ability to configure two specific timeouts in relation
to IIS. These are referred to as the session timeout and script timeout values.
They are configured when a mail user first loads the web mail
application.

The setting for the script timeout is typically not related
to session timeout issues. In any case, the default value for the script timeout
is 30 minutes, and can be changed via the registry. The value for the IIS
MMC can also be configured (which will override the setting MailEnable
applies).